1. Field of the Invention
The present invention relates to a voltage converting device and electronic system thereof, and more particularly, to a voltage converting device having a self-reference feature and realized in a Complementary metal-oxide-semiconductor (CMOS) process and electronic system thereof.
2. Description of the Prior Art
In an integrated circuit, a voltage regulator is a negative feedback circuit for generating an accurate and stable voltage. The voltage outputted by the voltage regulator is utilized as a reference voltage or a supply voltage of other circuits in the integrate circuit, generally. According to different voltage requirements and different features of components of the integrated circuit, the integrated circuit needs multiple voltage regulators to generate different supply voltages.
Please refer to FIG. 1, which is a schematic diagram of a conventional electronic system 10. The electronic system 10 may be an integrated circuit and comprises a supply voltage generating unit 100, a positive voltage circuit 102, a voltage range converting circuit 104 and a negative voltage circuit 106. The electronic system 10 utilizes the positive voltage circuit 102 operated between a positive supply voltage VDDP1 and the ground voltage GND and the negative voltage circuit 106 operated between the ground voltage GND and a negative supply voltage VDDN1 to generate a positive output signal VOUTP and a negative output signal VOUTN corresponding to the positive output signal VOUTP, respectively. Since an electronic component is damaged when the voltage across the electronic component exceeds a breakdown voltage of the electronic component, the electronic system 10 needs to use the voltage range converting circuit 104 as a buffer, for performing conversions of voltages and signals. The voltage range converting circuit 104 operates between a positive supply voltage VDDP2 and a negative supply voltage VDDN2, wherein the positive supply voltage VDDP1 is greater than the positive supply voltage VDDP2 and the negative supply voltage VDDN1 is smaller than the negative supply voltage VDDN2. In other words, the operational voltage range of the voltage range converting circuit 104 crosses positive and negative voltage range and overlaps the operational voltage ranges of the positive voltage circuit 102 and the negative voltage circuit 106.
Generally, the electronic system 10 only has an external system voltage VDDE as the power source. The electronic system 10 needs to use the supply voltage generating unit 100 for generating the supply voltages required by the positive voltage circuit 102, the voltage range converting circuit 104 and the negative voltage circuit 106. Thus, the supply voltage generating unit 100 needs at least four voltage regulators to generate the positive supply voltages VDDP1, VDDP2 and the negative supply voltages VDDN1, VDDN2. When the number of the functions of the electronic systems 10 increases, the number of the voltage regulators needed by the electronic system 10 increases. In other words, the electronic system 10 needs more voltage regulators to provide required supply voltages. However, the voltage regulator needs external inductors or external capacitors, generally, to provide a stable and accurate supply voltage. The manufacture cost of the electronic system 10 significantly increases if the number of voltage regulators arises. Moreover, at the moment the external system voltage VDDE turns on the electronic system 10, time differences are generated between the times of each supply voltage (e.g. the positive supply voltage VDDP1, VDDP2 and the negative supply voltage VDDN1, VDDN2) are generated. The time differences may cause latch-up in the electronic system 10.
On the other hand, since the supply voltages of the electronic system 10 are multiples of the external system voltage VDDE (e.g. the positive supply voltage VDDP1 may be a product of the external system voltage VDDE and 1.5, and the positive supply voltage VDDP2 may be half of the external system voltage VDDE), generally, the supply voltages of the electronic system 10 vary with the external system voltage VDDE, resulting in the supply voltages deviating from the original design values. For example, when the external system voltage VDDE is provided by a battery, the external system voltage VDDE varies with the charge storage level of the battery. The electronic system 10 needs a reference circuit to provide a reference voltage which does not vary with the external system voltage VDDE for stabilizing the supply voltages at the original design values via the feedback mechanism.
Generally, the reference circuit for providing stable reference voltage can be realized by a bandgap circuit consisting of bipolar junction transistors (BJT) realized in CMOS process or CMOS devices. The bandgap circuit realized by the BJT is not sensitive to the process variation, but the BJT of the CMOS process easily encounters latch-up when the power source turns on. Moreover, the component features of the BJT of the CMOS process also cause limitations when designing integrated circuit. Although the bandgap circuit can replace the BJT by the metal-oxide-semiconductor field-effect transistor (MOSFET) operating in sub-threshold zone, the temperature coefficient of the MOSFET operating in sub-threshold zone is easily affected by the process variation, resulting the reference voltage deviates from the design.
Besides, the bandgap circuit only generates a constant reference voltage without the ability of driving loadings. In such a condition, the reference voltage generated by the bandgap circuit needs additional voltage regulators for generating the reference voltages in different voltage levels and having the ability of driving loadings. The manufacturing cost of the electronic system 10 is increased and the design of the electronic system 10 therefore becomes complicated. Thus, how to simplify the circuits for generating the supply voltages in the electronic system becomes an important issue in the industry.